The present invention relates to a method and a device that is reactive and consumes very little energy, for continuous optimization of the compression ratio, particularly of alternating-piston engines. This invention is particularly relevant to increasing the energy efficiency of engines that are not used continuously at full load or that use multiple fuels with different octane ratings. This invention is compatible with a very low pollution level and adapts in particular to alternating-piston engines whose cylinders are disposed flat, either in a xe2x80x9cVxe2x80x9d configuration or in-line. In the present document, the term xe2x80x9ccompression ratioxe2x80x9d designs the geometric compression ratio of an alternating-piston internal combustion engine.
Continuous optimization of the compression ratio is relevant in reducing fuel consumption and the contribution to the greenhouse effect for applications where the engines are not at full load and for engines that use multiple fuels with different octane ratings.
Combustion in spark ignition engines operated at very low loads is more complete when the compression ratio is optimized during operation. Carbon monoxide, hydrocarbon, and particle emissions are hence lower.
Continuous optimization of the compression ratio is relevant in keeping an engine in the spark ignition operating mode by compressing a premixture of fuel and oxidant. Such a method of operation, described in particular in patent WO 99 42718 A, enables a very low nitrogen oxides emission level to be reached.
Moreover, optimization of the compression ratio is compatible with the usual systems for reducing nitrogen oxide emissions such as exhaust gas recycling (EGR) systems or nitrogen oxide catalysts.
The prior art already contains a number of solutions for modifying the compression ratios of alternating-piston engines. A summary is provided below.
One known solution for changing the compression ratio consists of placing a moving part in the cylinder head. Patent WO 99 13206 A describes one example. This part must slide in the presence of gases undergoing combustion. The interstices must be minimized to limit unburned particles. The moving part is placed in the cylinder head with the valves and participates in the shape of the combustion chamber.
U.S. Pat. No. 2,770,224 refers to an engine whose block, divided into two articulated parts, enables the distance between each piston and the corresponding cylinder head to be varied. Patent WO 93 23664 A discloses a solution for controlling this type of device. The separation force of the two parts of the engine block is used to reduce the compression ratio and store energy. The stored energy is then used to increase the compression ratio when the engine load decreases. The operating hysteresis is limited by the energy supplied by an activator. The engine block is designed and dimensioned to provide sufficient mechanical strength for the link between the two articulated parts of the engine block, and to minimize vibrations.
Patent WO 95 29329 A describes a device having two cams at the head of each connecting rod. The angular setting of these two cams is a function of the engine load and enables the distance between each piston and the corresponding cylinder head to be modified.
One category of solutions is to modify the length of the connecting rod, for example by adding an articulation modifying the straightness of the connecting rod. Patents EP 0 520 637 A and DE 195 02 820 A belong to this category of solutions. The additional parts that transmit forces between the pistons and the crank pins must be designed and dimensioned as a consequence to ensure the required reliability.
Another category of solutions adapted more particularly for in-line engines includes cams mounted on the crankshaft bearings to modify the distance between the crankshaft axis and the cylinder head. Patents FR 2,669,676 A, U.S. Pat. No. 1,872,856, U.S. Pat. No. 4,738,230, and DE-A-3,601,528 describe devices that may be classified in this category. The rigidity of the crankshaft bearings must be compatible with the required service life. Patent DE 297 19 343 U discloses a device for ensuring the alignment between the crankshaft and the transmission.
A crank pinion mounted at the end of the crankshaft meshes with an internally toothed wheel mounted on the flywheel. The teeth of these gears must withstand the rotary vibrations of the crankshaft and meet service life and noise requirements.
Patent WO 91 10051 A refers to a cam placed between the foot of each connecting rod and the corresponding crankshaft crank pin, whose angular setting is achieved by means of gears. The gears must be designed and built to and meet service life and noise requirements.
Patents JP 7527/90, JP 7528/90, JP 125166/90, and EP 0 438 121 A1 relate to a cam mounted either at the head or at the foot of each connecting rod, whose angular position is hydraulically actuated and stabilized by a removable finger. This finger must be designed and dimensioned to ensure the required reliability and service life. This device enables the compression ratio to be adjusted discontinuously.
The invention relates to a method and device for continuous optimization of the compression ratio within ranges determined by design, particularly for in-line, V, or opposed engines. The invention has the advantage, as far as the necessary technologies are concerned, of being compatible with the technologies currently used for cylinder heads, cylinder blocks, crankshafts, and their connections with the transmissions. It also has the advantage, as far as its implementation is concerned, of allowing the use of technologies similar to technologies used in alternating-piston engines that are well understood and are of proven reliability. The particular embodiments according to the invention have other advantages listed in this description.
The present invention applies to internal combustion engines with alternating pistons driven by a crankshaft. Each of these engines has one or more combustion chambers and a crankcase. The crankcase is defined in the present description and claims as the part (or rigid assembly of parts) that provides the link between the combustion chamber or chambers and the fixed parts of the crankshaft bearings. The axis of rotation of the crankshaft journals is called the crankshaft axis. These engines also have one or more cylinder heads that is/arc distinct from or integral with the crankcase. Each piston is connected to a crankshaft crank pin, particularly by a piston axis, a connecting rod, and a cam. This cam is located between the foot of the connecting rod and the crankshaft crank pin that corresponds to a given combustion chamber. The change in angular setting of one of the cams relative to the crankcase brings about a change in the compression ratio of the corresponding combustion chamber. In the description and claims of the present invention, a piston is at the top dead center for each complete revolution of the crankshaft when the distance between this piston and the corresponding cylinder head is at a minimum.
The method according to the invention consists of modifying the compression ratio of each combustion chamber by carrying out the functions described below, with possible differences included within tolerances compatible with correct operation and implementation options:
moving a point in a plane orthogonal to the crankshaft axis;
maintaining a geometric axis in a plane orthogonal to the crankshaft axis and articulating this geometric axis around the point where the projection of the point referred to in the previous subparagraph intersects the plane of rotation of this geometric axis;
choosing another geometric axis contained in a plane also orthogonal to the crankshaft axis and maintaining parallelism and a fixed distance between the two aforesaid geometric axes so that their direction when the piston is at the top dead center and the direction of movement of the point referred to in the first subparagraph above are different;
maintaining a fixed relative position between the geometric axis chosen according to the previous subparagraph and the cam located between the foot of the connecting rod and the crank pin of the crankshaft.
The terminology defined below will be used in the remainder of this description to designate the points, planes, and geometric axes of the method according to the invention described in the previous paragraph:
the point moved in a plane orthogonal to the crankshaft axis will be called the moving point;
the plane orthogonal to the crankshaft in which the moving point moves will be called the moving point plane;
the first geometric axis defined in the method according to the invention will be called the articulated axis;
the plane orthogonal to the crankshaft axis containing the projection of the moving point articulating the articulated axis and in which the articulated axis is maintained, will be called the projection plane;
the projection of the moving point on the projection plane will be called the articulation point;
the second geometric axis defined in the method according to the invention will be called the axis attached to the cam;
the plane orthogonal to the crankshaft axis containing the axis attached to the cam will be called the lever plane.
For engines having several combustion chambers, the method according to the invention is applied to each combustion chamber whose compression ratio is to be modified.
The method according to the invention will be better understood by reading the seven paragraphs below. These seven paragraphs relate to the method according to the invention for modifying the compression ratio of a single combustion chamber of the engine.
The embodiments of the invention relate to the exact geometric characteristics referred to in the method. However, any reduction to practice is manufactured with differences from the exact values given. These possible differences from the exact geometric characteristics are included in tolerances compatible with implementation options according to the method and allow correct operation of the engine.
The moving point plane, the projection plane, and the lever plane are defined relative to the crankshaft axis. The crankshaft and its axis are unable to move axially translationally relative to the crankcase. The moving point plane, the projection plane, and the lever plane thus always have the same relative positions with respect to the crankcase. The movements of the articulated axis, of the axis attached to the cam, of the moving point, and of the articulation point are movements relative to the crankcase.
The articulated axis and the axis attached to the cam are kept parallel to and equidistant from each other. Each of these two axes is contained in a plane orthogonal to the crankshaft axis. Neither of these two axes changes its plane during the method according to the invention. These features have in particular the consequences listed below, obtained in practice with possible differences compatible with correct operation and implementation options:
the articulated axis and the axis attached to the cam have the same direction;
any movement of the articulated axis is possible only in the projection plane;
any movement of the axis attached to the cam is possibly only in the lever plane;
any translation of the articulated axis with a component perpendicular to itself drives the axis attached to the cam along this component;
any translation of the axis attached to the cam with a component perpendicular to itself brings about translation of the axis articulated along this component;
any rotation of the axis articulated around the articulation point brings about a rotation with the same angle of the axis attached to the cam around the projection orthogonal to the articulation point on the lever plane;
any rotation of the axis attached to the cam around the axis of the corresponding crank pin of the crankshaft brings about an identical rotation of the articulated axis;
the relative translations between the articulated axis and the axis attached to the cam parallel with each other are neither prohibited nor prescribed by the method according to the invention so that two cases are possible: either the application allows the translations referred to in this subparagraph or the application does not.
The method according to the invention is hence compatible with devices for which operation brings about a change in the distance between the articulation point and the axis of the corresponding crank pin of the crankshaft.
The method according to the invention is also compatible with devices that do not enable the distance between the articulation point and the axis of the corresponding crank pin of the crankshaft to be varied.
The angular setting of the cam on its crank pin depends on the angular setting of the axis attached to the cam and the axis articulated with respect to the crankcase. To two distinct positions of the moving point in the moving point plane, the direction between these two distinct positions of the moving point not being parallel to the direction of the articulated axis and the axis attached to the cam when the piston is at the top dead center, there correspond two different angular settings of the articulated axis, of the axis attached to the cam, and of the cam, relative to the crankcase. To these two angular settings there correspond two different compression ratios, except for specific cases where these two angular settings correspond to the same distance between the crankshaft axis and the axis of the connecting rod foot.
This paragraph lists several specific applications of the method according to the invention given as non-limiting examples. For the first application, the moving point and the articulation point are in the same plane perpendicular to the crankshaft axis. For the second, the moving point is equated with the articulation point. For these two particular applications, the moving point plane is equated with the projection plane. For the third, the articulated axis and the axis attached to the cam are in the same plane perpendicular to the crankshaft axis. For the fourth, the articulated axis and the axis attached to the cam are equated. For these latter two applications, the projection plane and the lever plane are equated. All the possible combinations between the particular applications referred to above are applications of the method according to the invention.
According to another feature, the moving point is driven translationally by a point whose movement has parallel components perpendicular to the moving point plane.
According to another feature, the method according to the invention also applies to internal combustion heat engines also having an electronic device for calculating the optimum control values for operation of these engines, sensors for measuring the values of physical magnitudes characterizing operation of these engines, and devices for adjusting the operating controls of these engines to the values calculated by the calculation devices referred to above. This method consists of three phases carried out during operation of the engines: the first phase consists of measuring the values of the physical magnitudes that characterize operation of these engines, whereby these physical magnitudes include the compression ratio, the second phase consists of calculating, as a function of the physical magnitudes measured in the first phase, the optimum values for the controlled engine parameters to maximize energy efficiency and minimize pollution, whereby these controlled parameters include the compression ratio, and the third phase consists, for each cylinder, of accomplishing the functions described below:
moving a point in a plane orthogonal to the crankshaft axis;
maintaining a geometric axis in a plane orthogonal to the crankshaft axis and articulating the geometric axis around the point where the projection of the point referred to in the previous subparagraph intersects the plane of rotation of this geometric axis;
choosing another geometric axis contained in a plane that is also orthogonal to the crankshaft axis and maintaining parallelism and a fixed distance between the above two geometric axes such that their direction when the piston is at the top dead center and the direction of movement of the point referred to in the first subparagraph above of this third phase, are different;
maintaining a relative fixed position between the geometric axis chosen according to the preceding subparagraph, and the cam located between the foot of the connecting rod and the crank pin of the crankshaft;
controlling the movement of the point referred to in the first subparagraph of this third phase to cause the compression ratio to approximate the optimum value calculated in the second phase.
For the other feature of the method described in the foregoing paragraph, the compression ratio is measured by measuring a physical magnitude enabling the compression ratio to be calculated, for example: measuring movement of the articulation point. The other physical magnitudes measured according to this method are parts of the physical magnitudes usually taken into account when controlling alternating-piston internal combustion engines. The controlled parameters of the engine for maximizing energy efficiency and minimizing pollution, other than the compression ratio, are part of the controlled parameters normally used in controlling alternating-piston internal combustion engines.
According to another feature of the invention, the method described above is supplemented by calculating, in the second phase: the quantities of air and fuel admitted for combustion as well as the angle at which combustion is triggered according to the values of the physical magnitudes characterizing engine operation in the first phase, particularly the compression ratio, and is also supplemented by, in the third phase, the control of devices for obtaining the quantity of admitted air, the quantity of admitted fuel, and the angle at which combustion is triggered, so that the values of these three parameters are made to approximate the values calculated in the second phase, particularly according to the compression ratio.
Metering the quantity of air admitted for low loads has several advantages. The temperature at the end of combustion may be lower, thus favoring service life, energy efficiency, and nitrogen oxide emissions control. This is also a relevant parameter for maintaining an engine in the spark ignition operating mode by compressing a premixture of oxidant and fuel. Note that metering the air admitted by adjusting the settings of the inlet valves is relevant for limiting load losses at admission.
The device according to the invention, built into an internal combustion engine with alternating pistons driven by a main crankshaft having a cam located between the foot of each connecting rod and the corresponding crank pin of the main crankshaft is characterized in that each cam located between the foot of each connecting rod and the corresponding crank pin of the main crankshaft is oriented with a rod articulated on a pivot.
According to a first list of additional features of the device according to the invention, for each cam located between a connecting rod foot and the corresponding crank pin of the main crankshaft, the rod is integral with the cam and part of this rod slides in a part articulated to the pivot axis. This pivot is fixed or articulated, either on a slide or on the articulated arms of a rocking arm. The slide or the rocking arm is guided by a guide system and held in position. The assembly is designed so that, during operation, the geometric characteristics included in tolerances compatible with the implementation possibilities, and with the correct operation of the device and the engine, are respected. These geometric characteristics are the following: the axis of the sliding part of the rod is in a lever plane perpendicular to the axis of the main crankshaft, the movements of the pivot, of the slide, or the articulated arms occur in planes perpendicular to the axis of the main crankshaft, and the axis of the pivot is parallel to the axis of the main crankshaft.
According to a second list of additional features of the device according to the invention, for each cam located between a connecting rod foot and the corresponding crank pin of the main crankshaft, part of the rod slides in a part integral with the cam. This sliding rod is also integral with a part articulated to the pivot axis. This pivot is attached or articulated, either on a slide or on the articulated arms of a rocking arm. The slide or rocking arm is guided by a guide system and held in position. The assembly is designed so that, during operation, the geometric characteristics included in tolerances compatible with the implementation possibilities, and with the correct operation of the device and the engine, are respected. These geometric characteristics are the following: the axis of the sliding part of the rod is in a plane perpendicular to the axis of the main crankshaft, the movements of the pivot or the articulated arms occur in planes perpendicular to the axis of the main crankshaft, and the axis of the pivot is parallel to the axis of the main crankshaft.
According to a third list of additional features of the device according to the invention, for each cam located between a connecting rod foot and the corresponding crank pin of the main crankshaft, the rod is integral with the cam and with a part articulated by the pivot axis. The pivot is attached to the articulated arms of a rocking arm. The assembly formed by all the pivots and all the articulated arms of the rocking arms enabling the rods integral with the cams that are located between the feet of the connecting rod and the corresponding crank pins of the main crankshaft to be oriented are designed to form an orientation crankshaft. Each pivot articulating the direction of a rod integral with a cam forms a crank pin of this orientation crankshaft and each articulated arm of the corresponding rocking arm forms a lever connecting this crank pin to the corresponding journal of this orientation crankshaft. The orientation crankshaft is guided and oriented by a guide system. This guide system has a frame articulated to an axis that is fixed relative to the crankcase and is held in position. The fixed parts of the bearings of the orientation crankshaft are integral with this articulated frame. The guide system and the orientation crankshaft are designed so that, during operation, the geometric characteristics included in tolerances compatible with the implementation possibilities, and with correct operation of the device and the engine, are respected. These geometric characteristics are the following:
the articulation axis of the frame is equated with the axis of the main crankshaft;
each pivot and the axis of the orientation crankshaft are parallel to the axis of the main crankshaft;
the movements of each pivot are executed in planes perpendicular to the axis of the main crankshaft;
the length of the lever of each crank pin of the orientation crankshaft is equal to the length of the lever of the corresponding crank pin belonging to the main crankshaft;
the orientation crankshaft is rotationally connected to the main crankshaft so that the crank pin levers of these two crankshafts are always parallel.
According to one embodiment of the device according to the invention, each cam located between a connecting rod foot and the corresponding crank pin of the main crankshaft is oriented with the aid of a rod articulated to a swivel joint. The other aforesaid features remain unchanged.
The device according to the invention or its structural variant described in the preceding paragraph, associated with any one of the three lists of above-identified additional features, meets all the requirements of the method according to the invention. The guide system, the pivot or swivel joint, and the slide or rocking arm defined above conform to the characteristics described in the method according to the invention for the moving point, the articulation point, the moving point plane, and the projection plane. The pivot or swivel joint forms an articulation point, and its movements and the movements of the slide or of each articulated arm of the rocking arm form planes perpendicular to the axis of the main crankshaft; these planes correspond to the definition of the projection plane and the moving point plane. Several slide and rocking arm points correspond to the definition of the moving point. The projection of the direction of the rod on the projection plane corresponds to the definition of the articulated axis. Movement of any point of the cam as the main crankshaft rotates defines a plane that corresponds to the definition of the lever plane. The projection of the direction of the rod on the lever plane corresponds to the definition of the axis attached to the cam.
According to a fourth list of additional features of the invention, the engine includes an electronic calculator. The position of the slide or the articulated arms, for each cam located between a connecting rod foot and the corresponding crank pin of the main crankshaft, is calculated by the electronic calculator, in view of the possibilities defined by the mechanical design of the engine. The fourth list of features described in this paragraph may complete the device according to the invention or its structural variant, taken alone or in combination with any of the other three lists of additional features given above.
According to another feature, an activator uses some of the enthalpy of the exhaust gases to contribute to modifying the compression ratio.
According to another feature, the device according to the invention, in any of the versions described above, incorporates the feature described in the previous paragraph.
The use of some of the enthalpy of the exhaust gases has the advantage that energy wastage through the exhaust system can be reduced, to activate the device modifying the compression ratio in order to improve the energy yield.
According to another feature, at least one turbine supplied with exhaust gases is used to modify the compression ratio of the engine.
According to another feature, the device according to the invention, in any of the versions described above, includes the feature described in the previous paragraph.
According to another feature, a hydraulic actuator actuates the device for modifying the compression ratio.
According to another feature, a gas cylinder acts on a booster cylinder to supply a hydraulic pressure to modify the compression ratio of the engine. This design offers greater choice in placement of the gas actuator.
According to another feature of the invention, the cams located between the feet of the connecting rods and the crank pins of the main crankshaft are joined to one or more fingers and this finger or these fingers are all oriented to a half-space defined by a plane integral with the cam, this plane containing the crank pin axis.
This design minimizes weight and space occupied.
According to another feature of the invention, two cams are joined with an angular setting such that the axes of their inside diameters are the same.
This design enables the compression ratio of two cylinders harnessed to the same crank pin of the main crankshaft to be modified.